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Focuser smoothness on C11

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#1 jeffk1965

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Posted 23 November 2005 - 09:35 AM

Hi everyone,

I recently purchased a C11S-GT (XLT) and tried it out for the first time last night. My first light is posted in a different posting if you would like to read it.

When focusing my new scope, I did notice that the focus knob is smooth for a few turns and then stiffens up a little and then becomes smooth again. It did this in both directions. It did not in anyway prevent me from obtaining best focus but I was wondering why it was not completely smooth throughout the range of focus?

I did try turning the knob all the way in both directions but the focus was still the same. Smooth for a few turns and then stiffening up for a few and then smooth again.

Is there anything I can do to make the focus smooth throughout the entire range of focus?

Thanks,
jeff

#2 JerryWise

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Posted 23 November 2005 - 09:40 AM

Hey Jeff. I just got a new C-11 too. I added a Losmandy plate and one of the screws just caught the mirror when moving through focus. You can tell if the mirror is dragging on something by looking in the EP as it moves over the area. Does the image shift when the focus knob gets tighter? If it doesn't its likely a rough spot on the jack screw moving the mirror. If it does something is binding it. The binding screw I had was very visible from the front of the OTA. I would EMail Celestron support too. They are very good (if a bit slow) in responding.

#3 jeffk1965

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Posted 23 November 2005 - 11:56 AM

The image shift with my scope is very minor. The thing is the focus knob gets tighter, then looser, then tighter again, and so on.

Thanks,
jeff

#4 jeffk1965

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Posted 23 November 2005 - 12:42 PM

Focuser problem fixed 100%!!!!

I just took another look at the focuser and turned it and noticed that the slight binding was not that bad. Nevertheless, I looked into the ota with a flashlight while turning the knob and did not see the edges of the mirror touching anything as I turned the focuser.

I pulled the focuser's rubber cover a little and when it moved back about 1/8" the focus was smooth throughout the entire range of motion. I pulled the rubber cover of the focuser off and turned the metal focusing knob and it was smooth. I then pushed the rubber cover all of the way on until it was flush against the ota and the focuser was tight when it turned in spots. It turns out that the rubber cover for the focus knob is slightly uneven where it touches the ota and this is what was causing the problem.

What an easy fix!!

I am really happy with the scope now!!

Jeff

#5 JerryWise

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Posted 23 November 2005 - 02:17 PM

Focuser problem fixed 100%!!!!

I just took another look at the focuser and turned it and noticed that the slight binding was not that bad. Nevertheless, I looked into the ota with a flashlight while turning the knob and did not see the edges of the mirror touching anything as I turned the focuser.

I pulled the focuser's rubber cover a little and when it moved back about 1/8" the focus was smooth throughout the entire range of motion. I pulled the rubber cover of the focuser off and turned the metal focusing knob and it was smooth. I then pushed the rubber cover all of the way on until it was flush against the ota and the focuser was tight when it turned in spots. It turns out that the rubber cover for the focus knob is slightly uneven where it touches the ota and this is what was causing the problem.

What an easy fix!!

I am really happy with the scope now!!

Jeff


Great job Jeff. Matter fact, think I'll walk over and check my cover now. With your discovery I might find the focuser is a FeatherTouch in disguise.

#6 garyc11

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Posted 23 November 2005 - 04:00 PM

you can get a fine focusing adapter from scopestuff for $20. it just slips over the focus knob.


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